Materials having a dispersion of substantially inert dispersoids distributed in a metallic matrix are known. An example is TD-nickel, in which thorium oxide dispersoid is distributed through a nickel matrix. The dispersoids improve the mechanical properties of the material by interfering with dislocation movement, particularly if the dispersoids are closely spaced, and also by inhibiting the movement of the grain boundaries of the matrix during elevated temperature exposure.
There are two primary techniques for producing such materials, mechanical alloying and spray forming. In mechanical alloying, the more widely used of the two approaches, the material of the metallic matrix is melted and solidified as a powder. One or more types of metallic powders are mixed with the dispersoid, and the mixture is mechanically deformed in a high-energy environment such as a ball mill. In the mechanical deformation, the largely nondeformable dispersoid is incorporated into the deformable metallic powder(s) by repeated fracturing and cold welding of the metallic powder particles with the dispersion contained at the welded interfaces. After the mechanical deformation, the mixture is consolidated. This approach requires lengthy and/or costly ball milling operations which can be prone to the introduction of defects into the mechanically alloyed material. Additionally, many metallic matrix materials that are otherwise of interest cannot be used in mechanical alloying, because they are not sufficiently malleable to cold weld to the dispersoids in the ball milling. The use of mechanical alloying is therefore limited primarily to lower-strength, higher-ductility metallic materials.
In spray forming, metallic material is melted and sprayed from a spray gun to solidify or partially solidify in a suitable inert atmosphere prior to being consolidated against a substrate. The dispersoid is added to the spray of the metallic material as it leaves the spray gun and is thereby mixed with the solidified metal. Spray forming can only be used in specialized circumstances, inasmuch as the process is limited to the use of dispersoids that do not react with or melt in the molten metal, the process is expensive, and it is difficult to control the size and spacing of the dispersoid. The microstructure is dominated by the solidification structure of the metallic material produced at rapid cooling rates.
There is a need for an improved approach to the preparation of articles having a metallic matrix with dispersoids distributed therein. The required improvements include reducing the manufacturing time, reducing the number of process steps, reducing the sources of contamination, and permitting the use of higher strength matrix materials in combination with fine dispersoids. The present invention fulfills this need, and further provides related advantages.